Natural fibers such as cotton, are subject to shrinkage as a result of washing and drying. Natural fiber thread, when used for the sewing of clothing and other articles is also liable to shrinkage. Accordingly, proposals have been made in the past for shrinking natural fibers both in the form of thread and when woven into fabrics.
Ideally, it would be possible to preshrink both the fabric and the thread so that no further shrinkage of any kind could take place.
In practice however it is well known that this cannot be achieved. Many manufacturers guarantee their products against shrinkage but in practice, experience leads to the conclusion that some degree of residual shrinkage will always take place, as a result of laundering.
In addition, the amount of shrinkage is not always equalized as between the fabric and the thread. Fabric which has been preshrunk, and is then sewn using a preshrunk or partially shrunk natural fiber thread, is usually subjected to laundering many times during use. As a result of laundering, further residual shrinkage takes place.
It is found that in many cases the thread is liable to shrink somewhat more than the fabric. In addition, the thread will invariably shrink along its length. Since the thread is passed repeatedly through the fabric, during sewing, the length of thread used to sew a particular seam, will be much greater than the length of the seam. Since the degree of shrinkage is dependent on the length of the thread, and where shrinkage of the thread and fabric take place as a result of laundering, it will be apparent that the actual length of shrinkage of the thread will be greater than actual length of shrinkage of fabric. As a result, this can cause creases or puckers in the fabric, caused by the increase in tension in the thread as a result of the shrinkage taking place.
One of the problems in the preshrinking of thread is that, for reasons of economy, the preshrinkage operation must be carried out on a continuous basis. If the thread is, for example, unwound from a spool, and is wound up on another spool, some degree of tension is liable to occur in the thread, which tension will tend to resist shrinking.
This is highly undesirable, since clearly in the preshrinking operation it is desirable to permit as much shrinkage as possible.
Another problem is, of course, the fact that during the sewing operation, considerable tension is applied to thread, which may in fact cause a slight increase in length. Any resultant further shrinking of the thread as a result of washing and drying, will thus be immediately noticeable as it causes creases or puckers in the fabric.
Clearly, it would be desirable if possible to allow some form of elasticity in the thread which would at the same time allow for the sewing operation to be carried out with the thread at the appropriate tension, and at the same time allow some degree of relaxation in the thread which would compensate for subsequent shrinkage during washing.
Further problems arise in regulating the preshrinking operation, to account for variations in thread content and fiber, and in regulating process conditions.